1. Field of the Invention
The present invention relates to a positive-temperature-coefficient thermistor heating device and a process for the production of the same.
2. Description of the Related Art
A positive-temperature-coefficient thermistor heating device of the related art, as shown in FIG. 6 and FIG. 7, was composed of a positive-temperature-coefficient element (PTC element) 91, a first electrode 8 formed on a planar manner (or in the form of a plane) on the two surfaces of the same, and a heat radiating means 93 having heat radiating fins 931 and a second electrode 932.
The PTC element 91 is made to emit heat by flowing a current between a heat radiating means 93, 93 provided on the two sides of the PTC element 91. The heat emitted by the PTC element 91 is radiated from the heat radiating fins 931 of the heat radiating means 93 through the first electrode 8 and second electrode 932, so this is used as a type of heater.
The above-mentioned applied current, as shown in FIG. 7, flows to the PTC element 91 only through the projections 81 of the first electrode 8 in contact with the second electrode 931.
Further, the first electrode 8 has a rough surface. This is because it is necessary, as mentioned above, to pass the above current between the first electrode 8 and the second electrode 932 and to bond the two by an electrically insulative adhesive 7. That is, electric conduction is obtained at the projections 81 of the rough surface, while the electrically insulative adhesive 7 is interposed in the depressions 83.
In the prior art, to form the first electrode 8 having the rough surface, there was proposed a process for flame spraying aluminum (Al) for formation of the first electrode on the surface of the PTC element 91 (Japanese Examined Patent Publication No. 4-4713).
There were the following problems, however, in the case of use of the above flame spraying process.
That is, the above Al flame spraying process does not give sufficient bonding to the surface of the PTC element 91. Therefore, it was necessary to perform pretreatment to roughen the surface of the PTC element in advance.
Further, even if trying to form a rough surface by flame spraying, the height of the projections would not become uniform.
Therefore, it was difficult to adjust the balance of the ratio of the projections 81 for application of current and the depressions 83 for interposition of the electrically insulative adhesive 7. As a result, the bonding was sufficient, but the conduction would be insufficient and the thermal output would be lowered, or conversely the thermal output would be large, but the bonding would be insufficient and therefore there would be peeling or detachment of the heat radiating means 93 from the PTC element 91.
Further, the work of flame spraying Al resulted in Al dust circulating in the workplace and therefore there was a danger to safety and sanitation and further a risk of accidents such as dust explosions.